Poorly Korg EMX1-SD - Please help me diagnose and fix it ** EDIT - NOW FIXED! **

****************** Now fixed by Nick at https://bmamps.com/ - Many thanks! ****************** I turned my Korg EMX1-SD on for the first time in a few months and it immediately started making this squealing noise from all audio outputs. The tone of the noise changes when the power supply cable is moved or the orientation of the whole unit changes. Could this indicate a possible loose component connection on the internal power supply? When the main volume knob is in the 10 o'clock position the noise fades considerably. Apart from the annoying noise the unit operates perfectly. To try and isolate what's causing the noise I've tried the following: 1. Using an alternative power supply 2. Using alternative phono cables 3. Disconnecting the tubes/valves 4. Operating all buttons and knobs on the device